2. What is a Rock?
• Naturally-occurring mixtures
of minerals, mineraloids, glass
or organic matter.

3. What is a Rock?
• Rocks are divided into 3
groups based on how they
were formed:
•IGNEOUS
•SEDIMENTARY
•METAMORPHIC

4. What is the difference
between a rock and a
mineral?
• Rocks are made up of ONE or
MORE minerals.

5. Once a rock is formed, does it
stay the same rock forever?
• NO!

6. • Rocks are continually changed by many
processes, such as weathering,
erosion, compaction, cementation,
melting, and cooling
• Rocks can change to and from the
three types

7. What is the process through
which rocks change?
• The Rock Cycle—earth materials
change back and forth among the
different types of rocks

9. • No set path a rock takes to become
another kind of rock

10. • “Ignis” = Latin for “fire”
• Formed from the cooling of either magma or
lava
• The most abundant type of rock
• Classified according to their origin and
composition

11. ORIGIN— Where rocks are formed
• Below ground = from magma (intrusive
igneous rock)
• Usually have LARGE crystal grains (they
cooled slowly)

12. Some have large & small crystals
(called porphyritic)

13. • Above ground = from lava (extrusive
igneous rock)
• Usually have SMALL or NO crystals (they
cooled too quickly)

14. Peridotite: Intrusive or
Extrusive? Why?

15. Granite: Intrusive or
Extrusive? Why?

16. Porphyry: Intrusive or
Extrusive? Why?

17. Obsidian: Intrusive or
Extrusive? Why?

18. COMPOSITION— What kind of
substances the rocks are made of

19. Basaltic Igneous Rocks —made
from lava/magma that is low in silica,
rich in iron and magnesium. Rocks are
dark-colored.

20. Granitic Igneous Rocks—
made from magma/lava high
in silica and oxygen. Rocks
are light-colored.

21. Andesitic Igneous Rocks—
have a composition between
basaltic and granitic.

22. Diorite

23. Basalt

24. Granite

25. • Formed from sediments
(rock fragments, mineral
grains, animal & plant
remains) that are pressed
or cemented together or
when sediments precipitate
out of a solution.

26. • These sediments are moved by wind,
water, ice or gravity.
• Sedimentary rocks represent 7% of the
Earth’s crust, but they cover 70% of the
Earth’s surface.
• Sedimentary rocks are fossil-carrying
rocks.

27. What turns sediments into solid rock?
• Water or wind breaks down and
deposits sediment (erosion &
deposition)

28. • The heavy sediments press down on
the layers beneath (compaction)

29. • Dissolved minerals flow between the
particles and cement them together
(cementation)

30. How can sedimentary layers help us
understand the age of fossils?
• As sedimentary rocks
are deposited, they
form horizontal
layers
• Scientists know that
the layers on top
(and the fossils in
the top layer) are
YOUNGER than the
fossils in lower
layers.

31. 3 Types of Sedimentary
Rocks:
• Clastic (also called Detrial)—made of
broken pieces of other rocks

32. Organic—remains of plants and animals
are deposited in thick layers
• Examples
• Fossil rich limestone is made from the
shells of ocean animals; used to make
chalk
3 Types of Sedimentary
Rocks:

33. • Chemical—minerals dissolved in
lakes, seas, or underground
water
3 Types of Sedimentary
Rocks:
Mineral crystals are made as the shallow water that has
flooded the bottom of Death Valley evaporates.
Click on image for full size (66K JPG)
Courtesy of Martin Miller, University of Oregon

34. Examples
• Limestone
made when
calcite
mineral
precipitates
from sea
water
• Rock Salt—
made from
evaporation
of sea
waters

35. • Rocks that have changed due to
intense temperature and pressure
• “Meta” means “change” and morphosis
means “form” in Greek
• Igneous, sedimentary and other
metamorphic rocks can change to
become metamorphic rocks

36. What occurs in the Earth to
change these rocks?
• Pressure from overlying rock layers
• High heat, but not enough to melt the rock
• Rocks may be flattened or bent or atoms may
be exchanged to form new minerals.

37. How are metamorphic rocks classified?
• Foliated—mineral grains are flattened
and line up in parallel bands
• Example: gneiss formed from
rearrangement of minerals in granite
into bands

38. How are metamorphic rocks classified?
• Non-Foliated—No bands are formed
• Example: marble formed from limestone

39. Where do metamorphic rocks
usually form?
• Where magma intrudes relatively
cool rock
• Near colliding plates (near
mountain ranges)
• Places that are covered miles
thick with other rock causing
pressure
• When hot water intrudes rock
• Where a meteorite strikes
Earth (rare)
• Where lightning bolts strike
rocks (rare)